The etching of circuit patterns on integrated circuit substrate materials has been accomplished in a number of ways. The most common method has been the use of wet chemical reagents in combination with a chemically resistant mask on the substrate surface to selectively etch the desired circuit pattern. The industry trend to smaller and smaller integrated circuit dimensions requires higher resolution of the etching profiles than is possible with wet chemistry because of the isotropic undercutting of the resistant mask when small ratios of linewidth to film thickness are required. Certain other limitations of wet chemical etching techniques have prompted the industry to investigate other methods to achieve high resolution pattern transfer. In particular, gas phase dry etching by radiation enhanced surface chemistry has been found to produce very highly resolved patterns. A number of mechanisms have been proposed to account for the high reaction rates achieved by these methods, but the fact that the substrate surface is made highly receptive to anisotropic etching by photon beams, sheaths in radio frequency plasmas or particle beams has spurred considerable research in the industry. At present, each of these radiation enhanced etching systems has disadvantages. For example, photon beams, generally in the ultra violet region, are expensive and of low reliability if laser technology is employed. Radio frequency plasmas achieve collimation of ions passing through sheaths and thereby achieve directional ion motion toward the intended substrate material. However, energetic ions also cause ion bombardment damage to the film or device being etched as well as undesired impurity sputtering from chamber walls. Electron beams with thermionic cathodes are not tolerant of reactive gases needed to perform the etching process and typically have small area coverage.
It is therefore an object of the present invention to provide an electron beam etching system in which undesired impurity sputtering is eliminated because in the present invention the energy flux to the substrate is provided by a beam of electrons instead of a beam of ions. It is a further object of the present invention to provide an electron beam etching system in which a parallel electron beam to accomplish substantially isotropic etching and a perpendicular electron beam to accomplish substantially anisotropic etching are combined to permit highly controlled etching of a substrate surface, allowing tailoring of the etching profiles. It is yet another object of the present invention to provide an electron beam etching system in which plasma parameters such as gas pressure, ion density, and electron temperature are generally more independently controllable than in conventional dry etching systems.
These and other objects are accomplished in accordance with the illustrated preferred embodiment of the invention by employing one or more large area electron beam guns to provide directed energy to the surface of a substrate and to dissociate molecular donors in the gas phase to create free radicals that react with the substrate to accomplish the etching process.